Project Bought a ZXR250C.

Ain't this just the cutest little thermostat you've ever seen? It's about the diameter of a 20c piece.

 

Today I got the bore gauge and micrometer out and measured the pistons and the bores. Everything came up well within spec.

Waiting on the good cylinder head and megazip order to arrive.

 

The person I bought this 2nd hand cylinder head off and I have very different definitions of 'serviceable' - this valve is totally stuffed, and the seat is not much better. Several other valves have started to receed into the seats when compared to their neighbours.



Along with this, the whole head had obviously been left out in the elements. One intake port was covered in scale and the valves/seats were rusted. It's also running different valve springs with less progression to them, and several shims were missing. The cams were also in a very sorry state. Not happy at all, it was a total waste of time and money.

I got several opinions on the cracks on my cylinder head from several mechanics at work, and a few of the TAFE motorcycle teachers. The consensus is that they are not enough to worry about. I have no other options at the moment anyway, unless someone has a reconditioned head sitting around rady to go.

I got the scraper out and went all the carbon in the exhaust ports. I think I literally doubled the surface area simply by scraping all this crap out. This was only the first go, there was carbon right up back to the valve seats.



After that, I went to lap the valves into their seats. The valve grinding compound had the cap left on it and had turned to powder. Great. Mixed some oil in and smushed it up back into a paste, back in business! I proceeded to lap all 16 valves in. The exhausts were a struggle because the tool to stick on the valve head was *just* small enough to grab the exhaust valves. Once some of the paste made its way onto the head, it would pop off and require cleaning to work again... but I got them all done.

I am now waiting on my megazip order to arrive so that I can assemble the cylinder head. At least I have all the shims ready to go.

 

I doubt it, since the tension would be around the crush washer.

I think it occurred from overheating, or the cooling system not functioning correctly in the past.

 

On the original head it is fairly clean, the 2nd hand one is rubbish however.

I will run a cooling system flush through the system after it's back together, then dump it and put fresh coolant in

 

Honestly, I feel like the best thing for me to do is just fix what I've got. Buying other used stuff is always a gamble.

 

The hot water & ct18 bath got all of the external grime and oil off. I've scraped all the carbon out and made sure none of it got anywhere it wasn't meant to. All I have left to do is oil stone the gasket surfaces and refit the valves with new springs.

And I'm trying to do this on the cheap

 

Yesterday I dragged the bike down from the upstairs workshop and down to my bench.



Cylinders honed.



Head assembled.



Pistons fitted.



Gasket surface pretty clean, but it got a go on the oil stone.





Cylinders and head fitted. The manual says to use two head bolts with their heads cut off, but it isn't necessary to do so. I used 4 head bolts in the corners and everything went pretty smoothly.



Assembled and timed with new shims fitted.






As it sits now, but with the cooling system back on.




Filled it with fluids and cranked it over til the oil light went out.


Then I started on the carbs. Replaced all jets/holders, float needles and seats, and replaced the needles. The carbs had N1QW needles on all 4 carbs, the keysters kits had different ones on inner and outer. In any case I have saved all the bits in case there are any issues.




Carbs are now ready to be fit and clamped, with a fuel supply I could then run it and bleed the cooling system. Work was closing so I packed up and left, should have it running monday after work.

 

All back together and running nicely, will get a video tomorrow. Was buried with bikes so didn't get a ride, that'll be for lunchtime tomorrow. Excited!

 

December next year, if I can't convince the RMS here that I am eligble now, long boring story I won't get into

 

Took the bike for a run-in on lunch time and on the way home today to get the rings bedded in (acceleration and deceleration).

Adjusted the mixtures to be on the rich side to be safe, as it was running lean after the initial run around the block. Needs another balance. I will get it on the dyno at TAFE. Also, the idle control cable unscrewed and fell out, threads on the carb body look crappy. Got it back in, but not working correctly. Can increase the idle but only decrease so far (throttle balance will help). Thinking about another set of carbs and transferring all the new bits over, I think these ones are flogged out.

 

Yet to have it out on the open road - will let you know after the weekend